Aqueous dispersion of ionomeric polyurethanes having a (per)fluoropolyether structure for use as coatings are known. These compounds can crosslink in a wide range of temperature, from 10° C. to 200° C., and provide for durable coatings.
Thus, EP 1369442 A (SOLVAY SOLEXIS S.P.A.) Oct. 12, 2003 discloses aqueous dispersions of ionomeric polyurethanes having (per)fluoropolyether structures with cross-linking agents which, when applied to various substrates, provide for cross-linked coatings endowed with high water and solvent resistance properties, low friction coefficients and anti-graffiti properties.
Moreover, WO 96/10595 (MINNESOTA MINING AND MANUFACTURING COMPANY) Nov. 4, 1996 discloses a two-part water-based composition prepared by mixing two aqueous compositions, one of them comprising a polyurethane prepolymer, said prepolymer optionally containing a segment notably selected from fluorinated-polyether diol segments and having both carboxylic acid and hydroxyl functional groups in an amount such that the acid number of the prepolymer ranges from about 10 to 100 and the average hydroxyl functionality of the prepolymer ranges from about 1.85 to 2.7, and, optionally, one or more acrylic polymers, the other comprising a cross-linking agent selected from polyisocyanates, blocked polyisocyanates and mixtures thereof. The final composition obtained upon cure exhibits high damping character and excellent scratch-resistance, mar-resistance and self-healing properties to be used as a coating. However, no mention is made therein of use of said cured composition as a decorative and protective coating.
A decorative coating is typically used for protecting architectural surfaces, in particular interior and/or exterior surfaces of buildings and surfaces of other physical structures notably including urban furniture, and interior and/or exterior surfaces of public transports.
Demand for protective coatings is still growing in the architectural field, wherein architectural surfaces, typically exposed to aggressive atmospheric pollutants and weather conditions, necessitate a long-lasting protection.
Masonry is commonly used for the walls of buildings, retaining walls and monuments. Bricks and concrete blocks are the most common types of masonry typically used. Extreme weather causes degradation of masonry surfaces due to frost damage. Moreover, masonry surfaces, because of their susceptibility to moisture absorption and retention, need to be protected to withstand the effects of corrosion, in particular in the case of reinforced concrete structures wherein the embedded steel reinforcing bars are typically corroded. Protective coatings are thus required which enable retaining durability of the overall masonry construction and breathability thereof in allowing trapped moisture to escape outside the coated surface while preventing more moisture from entering.
As graffiti paints also represent a major and increasing danger to buildings and heritage monuments made up of stones, bricks and mortars other than to public transports, protective coatings are particularly demanded which are further suitable for protecting surfaces against graffiti markings.
Anti-graffiti coatings may be classified into sacrificial and semi-sacrificial coatings, which are applied to a surface and then removed taking the graffiti with them, and permanent coatings, which prevent graffiti paints from adhering to a surface.
A sacrificial coating forms a clear coat barrier over the wall or surface being protected. If the surface is vandalized, the coating can be removed using a high-pressure washer taking the graffiti with it. The coating then must be reapplied. The materials used to make a sacrificial coating are usually optically clear polymers such as acrylates, biopolymers and waxes. These polymers form weak bonds with the substrate to allow for easy removal. A semi-sacrificial coating known as a safety shield acts as a penetrating sealer on the wall or surface protecting the surface pores. If the surface is vandalized, the coating can be removed using a combination of graffiti remover and high-pressure washer. The anti-graffiti safety shield is generally reapplied.
Permanent coatings work by creating a protective surface which makes graffiti paints unable to adhere to the surface. After the surface has been vandalized, the graffiti paint is typically removed by a specific remover. The underlying surface and the protective coating will remain undamaged.
Some of the types of permanent coatings notably include those based on fluorocarbon chemicals. Fluorinated coatings are some of the most effective in the field of graffiti prevention especially due to hydro- and oil-repellence properties thereof. These coatings also have the added benefit of being chemically inert as well as very durable. Unfortunately, they are also expensive and can be difficult to apply.
The need was thus felt to have available a composition based on cross-linkable ionomeric polyurethanes having a (per)fluoropolyether structure which would enable obtaining coatings endowed with the following properties:                low VOC (Volatile Organic Compound) content,        chemical resistance,        resistance to UV aging and weathering,        hydro- and oil-repellency,        stain- and soil-release,        breathability,        good adherence to any kind of substrates even after several cleaning cycles,        excellent anti-graffiti properties,        
to be successfully used for on-site outdoor and indoor applications as being easily cleanable under non-aggressive cleaning conditions.